This invention relates to a method and apparatus for pulse data transmission through water return cables, and more particularly for such cables payed out to a selectable length within a predetermined range from a coil in an open pack attached to an electronic package with a substantial portion of the cable remaining coiled in the pack.
A sonobuoy is a typical instrumentation system which may employ the present invention to great advantage. Sonobuoys were developed as submarine detectors to be dropped from aircraft, or otherwise deployed in the ocean, but the present invention is not limited to submarine detection applications. It is applicable to any instrumentation system for commercial or scientific applications, such as oil exploration. Consequently, although the present invention will be described in a specific embodiment with reference to a sonobuoy, it is not intended that the claims be construed as limited to a sonobuoy.
An air-dropped sonobuoy assembly is comprised of a battery-equipped and weighted instrumentation package. Attached directly to the package is a cable pack which pays out a single-wire cable until the desired depth is reached. The payed out portion of the cable between the buoy and the cable pack is selectable over a wide range (e.g., 4,000 to 16,000 feet) and may be determined by a clock in the instrumentation package which begins operation when the batteries are activated by sea water, thus establishing the depth of the instrumentation package from predetermined rate of descent data. Alternatively, a pressure transducer in the instrumentation package may be used to sense the desired depth pressure and stop the cable pack from paying out additional cable. In either case, there is usually a significant length of coiled cable remaining in the pack.
This practice of providing sufficient cable for a wide range of depths presents two significant problems. The first problem is to provide a means for terminating the process of paying out cable. The second problem is to provide a means for bypassing the coiled cable remaining in the pack. A solution to this second problem is significant because transmission through the coiled portion of the remaining cable, plus the payed out length of cable, may require an extremely elaborate and expensive electronic transmitter and receiver to compensate for the poor frequency response and distortion of the coiled cable in the pack. Experience has demonstrated that typical pulse data transmission through the coiled cable in the pack is too complex and costly to develop for the contingency of most of the cable remaining in a coil inside the pack and very little payed out. It is preferable to simply bypass the coiled cable in the pack.
One electrical-bypass technique for solving the second problem is to mechanically penetrate the cable to achieve electrical contact while maintaining electrical isolation from the water with a pressure seal. Mechanical penetration with electrical isolation from water must be achieved as an automated process. That poses yet another problem. The significance of this other problem can be appreciated when it is considered that the return path for the signal transmitted over the cable is through the ocean water and it is recognized that undesirable electrical leakage current from the insulated conductor to the water at the point of penetration will short circuit the signal cable, or greatly increase power expenditure, and also quickly erode the conductor and/or penetrator by electrolysis.